The present invention relates to rubber reinforced styrenic polymer resins More particularly, the present invention relates to such rubber reinforced resins having improved weather resistance and physical characteristics. In one embodiment, the present invention relates to an improved weatherable rubber reinforced styrene-acrylonitrile resin.
It is previously known in the art to prepare rubber modified resins wherein the rubber comprises a grafted copolymer of ethylene, propylene and optionally a copolymerizable diene monomer. Such rubbers are known as EPDM rubbers. In U.S. Pat. No. 3,489,821 a blend comprising an EPDM graft terpolymer and a hard matrix resin is disclosed. At Col. 7, line 31, the reference teaches that the graft copolymer resin blend may be mixed with other resins and/or rubbers
In U.S. Pat. No. 3,576,910, there is disclosed an ABS polyblend comprising a matrix copolymer of styrene and acrylonitrile and grafted rubbers wherein the grafted superstrate consists at least principally of a monovinylidene aromatic hydrocarbon and an unsaturated nitrile, i.e., styrene acrylonitrile copolymer. Suitable rubbers for use in the polyblend include diene rubbers, acrylate rubbers, polyisoprene rubbers and mixtures thereof.
U.S. Pat. No. 4,585,832 disclosed weather and impact resistant resins containing both a grafted acrylate rubber and a different grafted rubber. The second rubber could be either an EPDM rubber or a diene based rubber. Amounts of acrylate rubber from 60 to 97% based on total grafted rubber weight were employed.
In U.S. Pat. No. 4,397,987 a polyblend comprising a nitrile rubber and an EPDM graft rubber was disclosed. In Table 9, Col. I, a blend of an ungrafted EPDM rubber and HYCAR 4041, an acrylate rubber, was prepared.
Organic polymeric materials are subject to thermal, oxidative and ultraviolet light degradation which exhibits itself in the loss of physical properties in the resin and in change of color. Generally resins containing rubbers with residual unsaturation are extremely sensitive to such degradation. Resins containing EPDM, acrylate or other saturated rubbers are generally more resistant to such degradation and are referred to as weatherable resins. Nevertheless a certain amount of resin degradation may still occur upon exposure to ultraviolet light even for such weatherable resins. Therefor, it is generally necessary to incorporate into polymeric materials certain stabilizers which retard the above decomposition and discoloration. A variety of compounds have been employed for that purpose including the well-known hindered phenols, hindered amines, benzotriazoles, phosphorus esters, and polyalkyl thiobenzenes disclosed in U.S. Pat No. 4,163,006.
In addition to additives used to inhibit polymer degradation as above described, different additives to improve polymer processing properties may also be incorporated into organic polymeric materials. Examples include plasticizers which are generally introduced into a polymer in order to reduce the glass transition temperature thereof and to promote improved stress relaxation characteristics. In Modern Plastics Encyclopedia, Vol. 64, No. 10A, October 1987, at page 168, suitable general purpose plasticizers are said to include the phthalate esters of higher alcohols and diols: trialkyl trimellitates; polymeric polyesters: epoxidized soybean oil: monomeric esters of aliphatic dicarboxylic acid: polyesters of dicarboxylic acids with various glycols; triphenyl phosphate: monomeric esters of aliphatic dicarboxylic acid, for example dialkyl glutarates, adipates: etc. The same reference at page 643 discloses that the various molecular weight polymeric derivatives of ethylene glycol are suitable plasticizers for use in cellulose nitrate polymers.